In some transient application it is required to run a certain cycle (e.g. an NEDC) several times. It would be desirable to specify the boundary conditions of the cycle just once and then obtain this data repeatedly. The modulo function of the user defined calculation controller can be used to accomplish this task very easily.
This example is based on the default example ExEngine_HYBRID_adv and shows how the user defined calculation object is used to take the time, then use the modulo function to compute the remainder when dividing by the cycle length and finally define the simulation parameters with the help of maps.
Keywords: simulation parameter repeat cycle boundary conditions
Usable from release: KULI 12
These examples show how to set up a component test rig for a cross flow heat exchanger in KULI with the possibility to accurately specify the boundary conditions.
In order to predict the performance of a given cross flow heat exchanger (e.g. a radiator), it is sometimes quite useful to model a component test rig in KULI. This is particularly useful if a user receives measurement data or a KULI file of a component and wants to observe how this component performs at certain boundary conditions. In order to accurately specify all inlet conditions (temperatures, flow rates, pressures, humidity) at the same time, different modeling is required depending on the way how the air flow rate is defined (mass flow or entry volume flow or entry speed). The models in this example demonstrate how this can be achieved. They can be used as templates for test rigs in KULI. The component itself and the boundary conditions can easily be exchanged.Usable from release: KULI 12
In modern cooling system applications sometimes a radiator (coolant-air heat exchanger) is used to cool-down air (instead of air cooling-down the coolant). This makes it necessary for the model to consider potential condensation effects in the air.
Specifically only a part of the cooling power of the coolant is sensible heat on the air-side, while the rest compensates the heat from the phase change of the condensing air humidity (latent heat). Accordingly also a condensate mass flow is calculated.
As the KULI radiator component does not have native support for these effects, this library example provides additional functionality using calculation controllers and two air-side heat sources / sinks.Usable from release: KULI 12
This Excel sheet can directly be used to generate the data for a single pass of a 2 layer Cross-Counter-Flow Cooler (radiator, charge air cooler or oil cooler).
In special cases a cooler consists of two layers behind each other. In KULI this can be modeled as two separate coolers connected in series. As usually pressure drop and thermal performance data are available for the whole component only, the target is to generate the data for a single pass of the heat exchanger. This package provides Excel sheets and KULI files to perform this task. The Excel sheets require the Excel Add-In “Solver” and “KuliAnalysis2”. A detailed workflow description is given as well.Usable from release: KULI 12
The COM interface, developed by Microsoft®, provides a standardized interface for programs to communicate with each other. KULI has a set of built-in COM commands, which allow other programs to run and control a KULI simulation.
The current example is an Excel sheet which is created for the control and post processing of the time dependent simulation of a cooling system. The certain benefit of this Excel sheet is, that no Visual Basic programming knowledge of the user is required. Input and output parameters of a KULI file can simply be defined in a list, where the parameters can be chosen from an interactive menu. The sheet allows access to standard KULI COM objects but also to components directly via the KULI Direct Access Interface.Usable from release: KULI 8.0-1.04
This subsystem demonstrates a possibility to model a 4 way valve with which branches of a circuit can be combined or separated.
The attached subsystem has two fluid input ports (in1, in2), two fluid output ports (out1, out2) and one controller input with two possible input values. Depending on the value of the controller input, either in1 is connected to out1 and in2 is connected to out2 (“direct” connection), or in1 is connected to out2 and in2 is connected to out1 (“indirect” connection). In this way two loops/branches of a cooling circuit can either be combined (by using the “indirect” connection) or separated (by using the “direct” connection).Usable from release: KULI 12
This subsystem demonstrates a possibility to model an electric motor with fluid cooling of both stator and rotor.
The built-in model of an electric motor in KULI assumes that the stator is (optionally) fluid-cooled whereas the rotor is not. The rotor is only connected to the stator via conduction. Some e-motor concepts however also include a water cooled rotor. The attached subsystem provides a method with which such a configuration can be modeled. The main idea is to connect the heat conduction connector of the rotor with a point mass in the fluid circuit that models the coolant within the rotor. The point mass itself has a very high heat transfer coefficient. The heat conduction component modeling the heat transfer between the rotor and the water has a heat conductivity coming from CFD analysis.Usable from release: KULI 12
With this model and in particular with this workflow a pareto front diagram can be created in KULI lab.
During the process of optimizing a cooling package, quite often some compromise must be accepted. If you want to improve one value, another one gets worse. So usually it is quite difficult to define what the “optimal” solution really is. The pareto front is a graphical way to illustrate the line of “best compromises” that can be achieved.
The example shows how to generate such a diagram with the help of Monte Carlo Simulation and the 2D diagram features in KULI lab. In this example we vary the oil flow rate and the length of the oil cooler with the aim to reach both a low entry temperature and a low pressure drop in the cooler. Obviously both targets cannot be minimized at the same time, so we would like to see which values can be reached and we want to identify the parameters with which such a good compromise can be achieved.
Usable from release: KULI 12
With KULI you can model cooling systems for railroad applications, which can be diesel or electrical powered. In this specific application you can find a roof mounted cooling system with three coolers. One low temperature circuit for cooling the electric and electronic parts, one high temperature radiator for engine cooling and one intercooler.
One can include different types of fans, hydrostatic, electric or mechanical driven. In the simulation one can control the speed of the fan very flexible depending on the requirements of the cooling system measured by sensors like in the real life. Of course the operating conditions e.g. driving up a high mountain or in hot climate conditions are considered in the cooling system simulation.
At the end of the various variants done in the concept phase to find the best configuration of all components one will get a virtual prototype of the whole cooling system for railroad applications, which you will produce only once in hardware to verify the KULI simulation results on the test bench and in build-in situation.Usable from release: KULI 11.1
One possibility to set a target temperature in the cabin compressors is to control the compressors piston displacement.
This example demonstrates how a subsystem including several calculation controllers can easily be added to an existing HVAC simulation system.
By adjusting the compressors piston displacement, the performance of the compressor is controlled. This controlling strategy is included in a subsystem which mainly consists of calculation controllers.
As a necessary input, the user has to define a required cabin temperature and the upper and lower limit for the piston displacement. The calibration coefficient is a kind of displacement offset for the controller, used in each simulation time step.
If the average cabin temperature exceeds the upper temperature limit plus the temperature tolerance, the max. piston displacement of the compressor is used.
In all other cases the displacement is reduced or increased by the calibration coefficient. Due to the change of the displacement in each simulation time step, a smooth control characteristic is created.Usable from release: KULI 9.1-0.01
This example shows how to find a suitable compressor ratio with the help of parameter variation and a stop controller.
The task of this example is to find the lowest compressor rpm that meets the desired performance results. In this example we assume that the task is to find the compressor rpm such that the evaporator air outlet temperature is at or below 5 °C. Since in reality sometimes only a limited number of distinct ratios between engine rpm and compressor rpm is available, parameter variation is used. In addition a stop controller is applied such that the parameter variation stops as soon as the first suitable solution is found. This avoids the unnecessary calculation of operating points when the solution has already been found. It is important to run the parameter variation with increasing ratio such that the first solution that fulfills the stop criterion is really the solution with the lowest possible compressor rpm.Usable from release: KULI 11
This example shows how to automatically stop a transient KULI simulation if a given signal has become stationary.
In this example a stop controller is used to check if a certain signal has converged. The convergence itself is checked with the help of a series of delay controllers and a calculation controller. So the signal value at the current time t and at the time steps t-10, t-20, t-30, t-40, and t-50 seconds are evaluated. If the difference between the maximum and the minimum of these values is smaller than the value specified in the stop controller, then the simulation is stopped. In the given example the stop criterion is 0.1 K.
The big advantage of using the stop controller is that you can specify a very long simulation time (in the simulation parameters) such that it is ensured that convergence will occur, but if the convergence occurs pretty early, then KULI stops and does not produce “unnecessary” simulation output.
The calculation of this convergence value is put into a subsystem such that it can easily be transferred to other models.Usable from release: KULI 11
With this model the porosity coefficients for the air side resistance of a radiator can be calculated. This makes it easier to use the same air side resistance of a radiator in KULI and in CFD.
In standard underhood CFD calculations the heat exchangers (radiator, charge air cooler, condenser, etc.) are modeled as porous media. If a radiator is available as a KULI file, then this KULI model can be used to obtain the required coefficients which define the resistance of the radiator in the CFD model. In StarCCM+© (from cd-adapco) the resistance is defined in the following way:
delta p / L = alpha * v^2 + beta * v
where delta p is the static air side pressure difference, L is the depth of the radiator, v is the velocity perpendicular to the radiator surface, and alpha and beta are the coefficients that need to be evaluated. The KULI model makes a parameter variation for the velocity, where the lower and upper bounds can be specified as constants (they are predefined with 1 and 10 m/s, which is a reasonable range for most applications). The velocity is converted into a volume flow with the help of the width and height of the radiator. An analysis controller is used to calculate the sum of the deviations between simulated pressure difference at the component and the pressure difference calculated with the approximation formula. The sum of all these deviations is then put into an optimization target which is set to be a minimum. The coefficients alpha and beta serve as optimization parameters. (Usually these coefficients are in a range of up to 1000 or at most 1500, so this can be taken as a range for the optimization parameters.)
The example can easily be modified to include different formulas for porosities as used by other CFD codes.Usable from release: KULI 10.1
Thermostat to control the mass flow through two different branches.
With the subsystem Thermostat it is possible to control the mass flows through two different branches. Over the temperature of the 1.PM fluid resistances are increased or decrease over 2D curves.
To adjust the behavior of the thermostat to your own thermostat the following parameters have to be adjusted:
Usable from release: KULI 9.1-0.01
This example shows how a simple steady states simulation for a steam circuit of a truck – using ethanol as working fluid – can be set up. It consists of the steam circuit itself (closed circuit), an exhaust gas circuit (as source of the heat) and an open water/glycol circuit which acts as heat sink (condenser). Two evaporators are used as heat sources – one in the EGR system and one in the main exhaust system.
The rankine circuit is – similar to the A/C circuit – a thermodynamic cycle. The principle works like this:
In a first step the feed pump provides the working fluid for the expansion device, whereby the steam valves are used for controlling this system. They can either set the exit temperature at the evaporator or a defined mass flow. In this example two valves are used: One for the exhaust gas recirculation path (EGR path) and one for the main exhaust gas path.
In a next step the evaporator transfers the energy from the hot exhaust gas to the fluid and changes the medium’s state from liquid to gaseous. This energy is converted in the expansion device (if not bypassed) to mechanical power and cooled down in the condenser (to guarantee a liquid state for the feed pump).Usable from release: KULI 10
This example shows how a simple steady states simulation for a steam circuit of a truck – using ethanol as working fluid – can be set up. It consists of the steam circuit itself (closed circuit), an exhaust gas circuit (as source of the heat) and an open water/glycol circuit which acts as heat sink (condenser).
The rankine circuit is – similar to the A/C circuit – a thermodynamic cycle. The principle works like this:
In a first step the feed pump provides the working fluid for the expansion device, whereby the steam valve is used for controlling this system. It can either set the exit temperature at the evaporator or a defined mass flow. In a next step the evaporator transfers the energy from the hot exhaust gas to the fluid and changes the medium’s state from liquid to gaseous. This energy is converted in the expansion device (if not bypassed) to mechanical power and cooled down in the condenser (to guarantee a liquid state for the feed pump).
Based on the 2 dimensional characteristic, a 3D profile can be created by rotating the symmetric profile around the central axis. Based on this Profile, the pressure distribution of the fan can be added to the cooling package. Due to the uneven flow distribution, the performance of the cooling system will be influenced.Usable from release: KULI 9.1-0.01
These Excel Input sheets can directly be used to create KULI component files for speed and stage controlled fans. Additionally exiting component files can be imported and edited without a regular KULI installation.
For the use of these templates, KULI CompInterface and KULI MediaX are required!
KULI’s hvac components like the evaporator are based on a combination of geometrical and test data. To achieve a good accuracy of the model, a successful calibration is obligatory. This virtual test bench provides a model that supports the user to find the ideal calibration factors.
The evaporator is a core part of each HVAC system. In KULI, the model of the evaporator is based on a combination of geometrical and test data. In a first step all available geometrical data is defined directly in the component. Next, the simulation model is calibrated based on these input values by the use of various fitting values. These values influence the pressure losses at the refrigerant side and at the air side. Additionally they also effect the heat transfer for the refrigerant side and the air side as well as the condensate mass flow (evaporator) . The calibration can be done automatically in the KULI component, but for getting even more accurate results (with respect on specific simulation points) this Excel-KULI Co simulation test bench can be used.Usable from release: KULI 9.1-0.01
Due to constructive and performance reasons, indirect charge air coolers are more frequently used in state of the art cooling systems. Therefore this example demonstrates how a CCFC can easily be included in a steady state simulation model, whereby a low temperature radiator is added in the frontend and the coolant cooled cross-counter flow cooler (CCFC) is mounted next to the engine.
The KULI file shows the simulation model of a passenger car, including the main cooling circuit with the heat input of the engine, a simplified oil circuit and both sides of the indirect charge air circuit.
The CCFC is based on measurement values and geometrical input, therefore the data input differs from the traditional charge air cooler. At first, the user has to set up the geometrical properties and the configuration of the layers. In a next step, the measurement data defining the heat transfer and the pressure loss must be entered. The data can be input in a single table (no need for additional cold measurements of the pressure loss). To use this data, a calibration is obligatory. For the best result, the user can choose between different calibration methods like linear, quadratic or cubic.
The calibrated CCFC is included in the charge air circuit (outer side) and in a low temperature coolant circuit, which is located in front of the main radiator.Usable from release: KULI 10
By the flow of electric current, the Peltier Element can be used for cooling/heating – similar to a traditional heat pump. Due the fact that for a good performance a high electrical conductivity but a very low thermal conductivity is required, semiconductors are usually used for such elements.
Basically this example demonstrates the use of a Peltier element in a steady state cooling system. The model consists of a cold and of a hot side, whereby electric current is used to cool down an air flow. Both sides of the element are connected by a heat conduction element with a very small lambda value. Keep in mind that due to the use in a steady state model, the point mass is only used for modeling the heat transfer, therefore the simulation ignores the thermal inertia.
Basically the amount of heat rejected / absorbed by each side is the sum of the Peltier effect (current [A] * temperature of the cold side [K] * alpha [V/K]) and half the Joule heat (0.5*current [A] * current [A] *resistance [Ohm]). Cause of the current being squared for the Joule heat, at a certain point increasing the current will lead to a reduced cooling effect (for high currents the cooling effect can even turn into a heating effect).Usable from release: KULI 9.1-0.01
In this example phase change material (PCM) is connected to a fluid circuit.
Phase change material can store a high amount of energy due to its very high thermal inertia. This energy can e.g. used for a fast engine warm-up, to provide cooling performance in the HVAC system (evaporator) while no compressor is available, …
For the modeling of the phase change material, a subsystem containing a network of controllers is included. Additionally a virtual point mass (Phase Change Point Mass, only for internal calculation) is created and directly connected to the point mass in the fluid network. The heat is set at this virtual point mass, which directly sets the temperature at the coolant side PM.
The basic idea is that the sensible heat is calculated and only this “effective temperature changing” value is set at the virtual point mass. To take care of the melting / solidification energy, the actual change of enthalpy is calculated by a continuous evaluation. If the enthalpy is below / above the hold point, the subsystem can use the cp values for these areas and calculate the temperature change.
For simplification purposes, the cp value for the solid and for the liquid phase is constant, the change of enthalpy due to the phase change is considered in the melting heat.Usable from release: KULI 9.1-0.01
Usually the pressure loss in a component placed in the air path depends on the resistance, the mass flow rate and the temperature. Anyhow it could be useful to set a constant pressure loss. This can easily be done by the combination of a calculation controller with a media controller.Usable from release: KULI 9.1-0.01
The first order lag element (PT1) is a common element of the measurement and control technology. It can be used for the damping of an input signal, like demonstrated in this example.
Beside the input signal, the constant “T”, which adjusts how quickly the output value reaches the input value after a time step, is a necessary input value. The bigger the value of T, the longer it will take.
In this example, the controller input signal for the valve position of a circuit is filtered by a first order lag element (PT1).
This element is modeled by using KULIs default calculation controllers and controlling elements. For a good overview, they are grouped in the subsystem “PT1 – Element”.
The time-discrete formula is included in the 1st calculation controller. Necessary inputs are the simulation time step, the current input value and the output signal of the former time step.
Additionally the constant T is used to adjust how quickly the output value reaches the input value after a time step.
The PID controller outside the subsystem is used to set the limits (in this example the valve opening / closing position is limited between 5 und 95 percent).Usable from release: KULI 9.1-0.01
This model demonstrates how the air path for a pusher fan can be modeled in KULI. The focus is on the high resistance of the hub, which influences the flow distribution. To take care of this effect, the air path is split in separate segments.
To model the high resistance of the hub, an equivalent area resistance located in the air path is modeled. Therefore the circular area of the hub must be converted in a rectangular area resistance. In our experience, the zeta value (dimensionless resistance) of the area resistance should be 3 times higher than the zeta value of the radiator next to the hub.
The air path is split into several segments. A part of the air mass flow passes the resistance, the rest flows by. Due to this uneven resistance characteristic, the resulting uneven air mass flow leads to a temperature distribution.Usable from release: KULI 9.1-0.01